What Strange Places This Adventure Has Taken Me

Who would have thought that in this, the year of our lord Two Thousand and Twenty Six, I'd be purchasing a pack of brand new cassette tapes.

The eagle-eyed among you might notice that these are Type I tapes and not the High-Bias Type II tapes that this 4-track recorder is designed to use. You see, this is deliberate: not only are the Type I tapes much cheaper, and thus less worrisome to mess around with, but the fact that they're the incorrect tape means that they'll have much more distortion than the correct Type II tapes.

And giving things a quick test, the audio I recored to this tape, when played back, sounds... really, really good. Like I've got some proper nice headphones and I can't hear a bit of distortion, hiss or really anything but the exact same audio pouring back into my ears that I recorded onto it.

That might sound like a good thing, but 90% of the point of buying this 4-track was to take advantage of its character and colouring of the audio, and if it's reproducing the input nearly perfectly then it's not exactly adding a whole lot of colour.

But all is not lost, there are techniques that can be employed to increase the distortion and noise levels. Turning off the dbx system, slowing the tape to 4.8 cm/s instead of the 9.5 cm/s setting, and messing up the gain staging and recording levels will do a lot to make the sound properly crunchy. And, honestly, being able to scale things down from a starting point of "almost CD quality" means I'll have lots of range to dial things in to my liking.

I do also have a Type II cassette on its way, which is about 3.5x the price of these Type I cassettes, so it'll be interesting to see if it responds differently to being driven into distortion.

I am kind of impressed, though. Having only experienced cassette tape through basic car head units, cheap walkman knock-offs, and bargain basement radio cassette players, I never really had the chance to experience the full quality that cassette tape could deliver.

Wibbly Wobbly

With the MC-505 up and running after the previous adventure with fixing its screen, I decided that it was time to tackle the wobbly knob-blies.

One of the tools/techniques that I didn't address in the video was using my vinyl cutter in order to cut out stencils of the reinforcement plate design so that I could check the dimensions against the actual system. This was a lot quicker and wasted a lot less planet-killing plastic than 3D printing out the pieces as I went.

This was made a bit more challenging than it might have otherwise been due to me using just some plain, lightweight printer paper, but I bought a brick of heavy card stock to use for the next project, which I'm sure won't take me 7-8 years to get around to using like this vinyl cutter has.

A Tale of Two Yamahas

I've been in a bit of a groovebox groove lately, what with stumbling across some good deals on an MC-303 and an MC-505, and wouldn't you know it but a Yamaha QY-100 popped up with my four favourite words attacked: For Parts or Repair.

The unit was reported as not booting up, and when I powered it on I could indeed verify that the screen just came up blank and the unit was unresponsive, however once I held down the right key combo I was able to get it into DFU mode (which stands for "Device Fucked Up Firmware Update") and so it likely just had some data corruption in its flash memory.

Oh and it's also missing the trim piece around the SmartMedia card slot.

I'll model up and 3D print a replacement for that bit later, after I make sure I can actually get this thing running.

So to fix the firmware corruption, all I should need to do is load up the firmware MIDI file into something like Sysex Librarian and pour it into the midi port once it's booted into DFU mode.

Except that actually doesn't work at all due to Sysex Librarian completely ignoring the midi message timing and blasting the entire file at full data rate while the system is busy doing stuff like pre-erasing the flash chip.

So instead I took the advice of Paul Carbone and downloaded XGWorks to my wintendo, an app that apparently hasn't been updated since the mid 90s, which is about the same time period as when this groovebox was made.

I gotta say, of all the MIDI playback programs in the world, this is one of them. I'm pretty sure that using another more modern midi player (rather than a sysex tool) would have also worked just fine, but the firmware update was already installing so I just went with it.

And about 20 minutes later: success!

So, onwards we go to Yamaha number 2, after a brief grass-touching break.

Grass: touched.

So again, this was just a coincidental find. I had been pondering the idea of picking up a 4-track cassette recorder like the (in)famous Tascam Portastudio 424, but since those have got a bit of a cult following they tend to command a bit of a premium on the used market these days.

However, Tascam wasn't the only company making 4-track cassette recorders, as you might have guessed by now, and the Yamaha MT4X was a direct competitor and generally an even match for the Tascam.

And wouldn't you know it, I heard those four sweet words: For Parts or Repair.

It was obviously filthy and the plastic was a bit scratched, and much to my dismay the input jacks seemed to have very poor connectivity. So, apart it comes.

Getting the main board out of a mixer like this is always a challenge, and Yamaha made this extra fun by using these plastic push-rivets to secure the rear face plate. Thankfully the center pin can be removed by just prying under the edge with a knife and then the rivet slides right out.

Naturally every knob has to come off, and after 30-odd years some of them are a bit more stuck than others. This is extra annoying since the knobs are recessed into the front panel by quite a bit. Thankfully I have a tool for that.

And then finally the main mixer board is out.

Time to give it cancer.

So with everything cleaned and lubricated, I reassembled the unit only to discover that the input jacks still had a dramatically poor connection. I poked around, scratched my head, and then realized that actually the mixer was just fine; it was the RCA to 1/4 TRS adapters I had used to connect my SK-88 Pro to the mixer which were to blame. Figures.

Anyway, I pulled up Amazon and ordered up some RCA to 1/4 TRS cables and threw the adapters in the trash, then gave the mixer a little spit-shine and I gotta say it came out looking pretty nice.

It could still use a bit more detailing but it's good enough for now.

And now I just need to find a cassette to stick in here... which will probably be its own adventure.

Five-Oh... Five

So my Roland MC-303 levelled up by a solid 202 to become a MC-505.

I had originally been looking to pick up either an MC-303 or an MC-505, and the latter tended to be quite a bit more expensive since it actually ended up getting used by some actual musicians from time to time, and was just largely a much improved instrument over the MC-303.

When I stumbled across a "For Parts or Repair" MC-303 selling for cheap I jumped on it and, as discussed previously, gave it a solid spit shine to bring it back to life.

But then just the other day I spotted a "For Parts or Repair" MC-505 for a very attractive price, low enough that I really had no excuse to not buy it, and so buy it I did.

Naturally it has a few issues that need addressing, such as the screen being in a pretty sorry state, which I fixed here:

It also needs some new switches, though oddly the main tact switches are doing fine. It's just the sequencer/key switches that are a little scratchy and are sometimes triggering when I let off the key. Furthermore, the volume control pot doesn't work, nor do two of the effects pots, both due to some damage to the front panel PCB. Finally, all the pots other than the volume and bass boost are feeling pretty wiggly.

But all that will be addressed in due time. First, though, I wanted to make sure that the firmware is up to date. To do this, you're meant to download a set of midi files that you play back into the box from a computer or sequencer. Simple enough, right?

Well it would be, except that somehow Roland messed up the .mid files and wrote the wrong length in the header. This means that basically every modern piece of midi playback software will simply refuse to load the file because it's detected as being corrupt.

To fix this, the easiest thing to do is to rewrite the header with a simple python script. Since I hate python I just yelled at the google search AI mode until it wrote it for me.

import os

def fix_midi_track_header(filename):
    with open(filename, 'rb') as f:
        data = bytearray(f.read())

    # Locate the MTrk (Track Chunk) marker
    mtrk_index = data.find(b'MTrk')
    if mtrk_index == -1:
        print(f"Skipping {filename}: No MTrk header found.")
        return

    # The length field is 4 bytes long, starting 4 bytes after 'MTrk'
    # Actual data length = Total file size - (Header + MTrk marker + Length field)
    # For MC-505 files (79081 bytes), this should be 79081 - 22 = 79059
    actual_data_len = len(data) - (mtrk_index + 8)

    # Convert the new length to 4-byte Big-Endian format
    new_len_bytes = actual_data_len.to_bytes(4, byteorder='big')

    # Overwrite the old length field (bytes 4, 5, 6, 7 after MTrk)
    data[mtrk_index + 4 : mtrk_index + 8] = new_len_bytes

    # Save as a new 'fixed' file
    new_filename = f"fixed_{filename}"
    with open(new_filename, 'wb') as f:
        f.write(data)
    
    print(f"Fixed {filename} -> {new_filename} (New Track Length: {actual_data_len})")

# Run on all .mid files in the current directory
files = [f for f in os.listdir('.') if f.endswith('.mid') and not f.startswith('fixed_')]
for f in files:
    fix_midi_track_header(f)

This script worked nicely, and I was able to import the files into SysEx Librarian and then play them back to the MC-505, and the system updated perfectly.

Making Waves

Right now my function generator only makes wave. As in singular, not plural. This is because it has only one output hooked up to only one DAC board.

But I'd like it to make waves, plural, and there's room on the front panel for a second set of outputs, and room inside for a second DAC board. So I got to wondering: can I simply install another DAC board to enable the second set of outputs? The internet holds no clues on this matter, and it's not addressed in any detail in the service manual.

So let's find out the fun way!

For the record, this board is HP part number 08904-60203.

And it's supposed to have a shield on the back but for some reason eBay scrappers always seem to pull it off and discard it, but oh well it'll be fine for my uses.

Anyway, as we can see it's identical to the one I already have.

So let's stick it in and see what happens.

Now I don't (yet) have a second pair of SMC to BNC cables, but the "Low" output is actually just a floating ground that you can bypass to chassis ground, so it's not essential for most of the uses I have, and certainly not essential for testing out if the two boards will work together, so I can temporarily reroute it to the second board.

The other connection I need is a 12 inch 34-pin ribbon cable, which is very easy to source.

Ideally this cable would have one of the connectors flipped around to the opposite side so that the ribbon cable exits the other side of the connector, but it'll work just fine as-is.

Routing this cable is probably the most difficult part of the install. I had to loosen both the DAC board and the main board on the other side of the chassis and then wiggle the cable in from the mainboard side.

But I got it in there.

Then it's just a matter of plugging the board in, snapping it into place on the standoffs, and we're ready to tickle it with electrons and see if it'll dance.

So good news off the bat, without any extra configuration it lets me now select Out2 as a destination.

And if I take a peek at the scope...

It is, in fact, making waves (plural)! Perfect.

Now this does leave one minor issue, which is that I don't have any 19mm spacers to go between the boards to prevent them from jiggling loose and shorting out against each other.

But then, I do have a 3d printer.

Uh, excuse me a moment...

Right, as I was saying, I do have a 3d printer.

So let's make it squirt out some plastic.

So why did I make these spacers hexagonal? Well the answer is simple: hexagons are bestagons.

Anyway, I'll trim away the brim and slide them down over the standoffs.

And then the second DAC board snaps into place without any danger of contacting the first.

I do still need to get a second pair of SMC to BNC cables but I can get to that whenever I feel like it. In the meantime, I'm calling this upgrade a success!

SK-88 Or Die

So I was messing around with my Roland SK-88 Pro this afternoon and noticed that a few of the buttons weren't as responsive as I might have liked them to be. This is really quite a common problem for electronics of this vintage, as the tact switches will oxidize over time causing their contact resistance to rise from a few scant milliohms to dozens or even hundreds of ohms.

Thankfully the fix is pretty simple: just unsolder the old ones and solder in some new ones. I'd picked up a pretty decent sized stash of compatible tact switches after replacing the ones on my MC-303, so there was nothing stopping me but time and motivation, and I found an ample supply of both this evening.

The original tact switches were a slightly different variety this time, having a round case instead of a square one, but the lead spacing (5mm) and height (5mm) was still the same and there was plenty of room on the PCB to fit the square ones.

The process went very smoothly and I'm happy to report that the new switches work flawlessly.

Lead, Free Solder

The synthesizer stack grows ever taller, this time with the addition of a Roland XV-5050 rack-mount module. It's much smaller than a synth with an attached keyboard as it's designed to be used with a separate external MIDI keyboard or sequencer, which I'll elaborate on in a future blog post.

For now, though, I need to get it to actually work as I did, of course, purchase it with those four magic words "For Parts Or Repair".

This time the culprit was lead-free solder leading to a manufacturing defect where a number of the pins on the DSP that runs all the audio weren't properly connected to the PCB. Thankfully I just got a fancy new soldering iron so this gave me a great excuse to take it for a spin.

The end result is a working module full of sounds that I will have a wonderful time exploring.